This invention relate to apparatus for measuring a predetermined data of a living tissue which is applied to an apparatus for measuring an oxygen saturation, an apparatus for measuring a dye dilution curve, as well as an apparatus for measuring the level of hemoglobin in tissues.
Apparatuses of the type contemplated by the present invention have heretofore been operated under the principle of a "pulse oximeter", namely, by using pulsations that occur in living tissues containing blood. However, this method of measurement involves difficulty and does not insure correct results when the pulsation is low. Further, the method is susceptible to subject movement since it relies upon small changes in signal.
Another apparatus used today is one that performs measurement with reference made to light that has been transmitted through an ischemic earlobe. However, this apparatus not only uses a complicated mechanism for causing ischemia in the earlobe but also requires great skill in performing that operation. Furthermore, errors can occur on account of such factors as tissue distortion during the step of causing ischemia.
Thus, the conventional apparatuses have had various problems including the failure to provide correct results with low pulsation, high susceptibility to subject movement, and the inherent need to employ cumbersome and, hence, error-prone operations of measurement.
The level of hemoglobin or blood in living tissue is an effective index for evaluating whether circulation in the tissue of interest is successful or not. If blood supply to the brain is impaired by increased intracerebral pressure, the brain tissue can be damaged irreversibly. In order to prevent this phenomenon, it is important to perform continuous monitoring of the level of hemoglobin or blood in tissue. However, no apparatuses have so far been available that yield quantitative values in the measurement of hemoglobin and blood levels in tissue.